(1) Field of the Invention
This invention relates to the recovery of hydrocarbons from geological formations, and more particularly to an improved process and apparatus for effecting secondary recovery of hydrocarbons from previously producing hydrocarbon bearing geological formations by the introduction of a gaseous stream to effect stimulation and/or fracturing and a gas generator assembly for producing such gaseous stream.
(2) Brief Descriptions of the Prior Art
The yields of hydrocarbons, such as gas and petroleum, from wells can be increased by stimulating and/or fracturing the formation so as to stimulate the flow of hydrocarbons in the well is known to those skilled in the art. Various formation stimulating and/or fracturing procedures have been proposed and many now are in use, e.g. treatments with various chemicals (usually acids in aqueous solutions), hydraulic fracturing in which liquids are injected under high pressure (usually with propping agents), explosive methods in which explosives are detonated within the formations to effect mechanical fracture, as well as combinations of such procedures.
Chemical treatments ususally involve the use of large volumes of chemicals which can be expensive and difficult to handle, and which pose problems of contamination and disposal. Hydraulic fracturing ordinarily requires that large volumes of liquids be made available at the well site and that equipment be made available for handling such large volumes of liquid. Again, there can be disposal problems, as well as contamination of the well. Explosive methods can be exceptionally hazardous from the standpoint of transporting and using the necessary explosives and present difficulties in controlling the effects of such a procedure.
Other suggestions for increasing the yield of existing wells entail heating the formation to induce the flow of hydrocarbons from the formation. Methods and apparatus have been developed by which various combustion devices have been lowered into the borehole of a well to attain heating of the formation adjacent the device. The effectiveness of such devices is limited by the necessity for fitting the devices into a borehole and then obtaining only more-or-less localized effects.
In U.S. Pat. No. 4,423,780 to Vigneri et al., there is disclosed a process and apparatus for increasing the yield of hydrocarbons from an underground hydrocarbon bearing well formation by placing and connecting a vertically-disposed gas generator in position outside the well for supplying heated gas under pressure to the opening of the borehole; essentially sealing the connection between the gas generator and the borehole opening so as to enable the establishment of elevated pressures within the well; operating the gas generator to inject gas into the well at a relatively high temperature, the high temperature being less than the thermal ignition temperature of the hydrocarbons in the formation; increasing the pressure within the well to an elevated relatively high pressure; and maintaining an elevated pressure in the well at least until the formation is fractured. Such process and apparatus while exhibiting a potential to improving the recovery of hydrocarbon from an otherwise uneconomically producing well, is inherently dangerous to operate presenting potentially hazardous operating conditions leading to explosive conditions. Additionally, the apparatus must be moved from site to site requiring considerable time and effort to connect same to existing well head with concomitant start-up problems.